Techniques for application of light in additive fabrication and related systems and methods

ABSTRACT

Techniques for illuminating a photocurable material within a build area of an additive fabrication device are described. According to some aspects, a light source is provided that can be moved alongside a build area, allowing light to be directed to any desired position within the build area by moving the light source. This configuration may also allow the distance from the light source to the build area to be substantially the same for each position across the build area by moving the light source whilst maintaining a fixed distance from the light source to the build volume. The described approach may allow for fabrication of larger parts in an additive fabrication device by expanding or eliminating the practical upper limit on the area of the build volume that can be imposed by use of a laser light source in such a device.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/163,403, filed Oct. 17, 2018, which claims the benefit under35 U.S.C. § 119(e) of U.S. Provisional Patent Application No.62/575,250, filed Oct. 20, 2017, and claims the benefit under 35 U.S.C.§ 119(e) of U.S. Provisional Patent Application No. 62/679,167, filedJun. 1, 2018, each of which is hereby incorporated by reference in itsentirety.

FIELD OF INVENTION

The present invention relates generally to systems and methods fordirecting a light source within an additive fabrication (e.g.,3-dimensional printing) device.

BACKGROUND

Additive fabrication, e.g., 3-dimensional (3D) printing, providestechniques for fabricating parts, typically by causing portions of abuilding material to solidify at specific locations. Additivefabrication techniques may include stereolithography, selective or fuseddeposition modeling, direct composite manufacturing, laminated partmanufacturing, selective phase area deposition, multi-phase jetsolidification, ballistic particle manufacturing, particle deposition,laser sintering or combinations thereof. Many additive fabricationtechniques build parts by forming successive layers, which are typicallycross-sections of the desired part. Typically each layer is formed suchthat it adheres to either a previously formed layer or a substrate uponwhich the part is built.

In one approach to additive fabrication, known as stereolithography,solid parts are created by successively forming thin layers of a liquidphotopolymer (e.g., a curable polymer resin), typically first onto asubstrate and then one on top of another. Exposure to actinic radiationcures a thin layer of liquid photopolymer, which causes it to harden andadhere to previously cured layers or the bottom surface of the buildplatform.

SUMMARY

According to some aspects, an additive fabrication device configured toform layers of solid material on a build platform is provided, eachlayer of material being formed so as to contact a container in additionto the surface of the build platform and/or a previously formed layer ofmaterial, the additive fabrication device comprising a container havingan interior bottom surface extending in a first direction and a seconddirection, perpendicular to the first direction, and a movable stageconfigured to move in the first direction, the movable stage beingarranged beneath the container and comprising a plurality of lightsources offset from one another along the second direction and operableto direct light through the interior bottom surface of the container.

According to some aspects a method of additive fabrication is provided,the method comprising moving, within an additive fabrication device, amovable stage beneath a container having an interior bottom surfaceextending in a first direction and a second direction, perpendicular tothe first direction, the container holding a liquid photopolymer, andthe movable stage configured to move in the first direction, the movablestage being arranged beneath the container and comprising a plurality oflight sources offset from one another along the second direction andoperable to direct light through the interior bottom surface of thecontainer, and directing actinic radiation from at least some of theplurality of light sources through the interior bottom surface of thecontainer to the liquid photopolymer held by the container, therebyforming a layer of solid material that contacts the interior bottomsurface in addition to the surface of a build platform and/or to apreviously formed layer of material.

The foregoing apparatus and method embodiments may be implemented withany suitable combination of aspects, features, and acts described aboveor in further detail below. These and other aspects, embodiments, andfeatures of the present teachings can be more fully understood from thefollowing description in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1A depicts illustrative LED arrays, according to some embodiments;

FIG. 1B depicts a cross-sectional view of an illustrative arrangement ofan LED array and an imaging lens, according to some embodiments;

FIG. 2 depicts a cross-sectional view showing operation of anillustrative arrangement of light sources and an imaging lens, accordingto some embodiments;

FIGS. 3A-B provide schematic views of a stereolithographic additivefabrication device, according to some embodiments;

FIGS. 3C-D depict an illustrative moveable stage that includes segmentedrollers, according to some embodiments;

FIG. 4 illustrates distortions in a surface of a container that mayoccur during operation of an illustrative stereolithographic additivefabrication device, according to some embodiments;

FIGS. 5A-C illustrate motion of an LED array coupled to rollers,according to some embodiments;

FIGS. 6A-C illustrate motion of multiple LED arrays coupled to rollers,according to some embodiments;

FIG. 7 illustrates a light source with a roller in a ring geometry,according to some embodiments;

FIG. 8 illustrates a light source and associated heat sink and coolingfan, according to some embodiments; and

FIG. 9A-B illustrate system components and operation of an illustrativeadditive fabrication device;

FIG. 10 illustrates a linear LED array extending across a build area andconfigured to move along an axis, according to some embodiments;

FIG. 11 is a block diagram of a system suitable for practicing aspectsof the invention, according to some embodiments; and

FIG. 12 illustrates an example of a computing system environment onwhich aspects of the invention may be implemented.

DETAILED DESCRIPTION

Systems and methods for generating and directing a light source in anadditive fabrication device are provided. As discussed above, inadditive fabrication a plurality of layers of material may be formed ona build platform. In some cases, one or more of the layers may be formedso as to be in contact with a surface other than another layer or thebuild platform.

To illustrate one exemplary additive fabrication technique, a so-calledinverse stereolithographic additive fabrication device (or “printer”) isdepicted in FIGS. 9A-B. Illustrative stereolithographic printer 900 isconfigured to form a part in a downward-facing direction on a buildplatform 904 such that layers of the part are formed in contact with asurface of container 906 in addition to a previously cured layer or thebuild platform. In the example of FIGS. 9A-B, stereolithographic printer900 comprises build platform 904, container 906, liquid photopolymer910, a laser 916, and a scanner system 918. The build platform 904opposes the floor of container 906, which contains liquid photopolymer910. In the example of FIGS. 9A-B, stereolithographic printer 900 isconfigured to form a part, such as the part 912 illustrated in FIG. 9B,in a downward facing direction on the build platform 904 such thatlayers of the part are formed in contact with a surface of container 906in addition to a previously cured layer or the build platform 904.

As shown in FIG. 9B, a part 912 may be formed layer wise within a buildvolume of the stereolithographic printer 900, with an initial layerbeing attached to the build platform 904. As referred to herein, a buildvolume is a volumetric region in an additive fabrication device in whichsolid material can be produced by the device by solidifying a liquid orotherwise. The container's floor may be transparent to actinicradiation, which can be targeted at portions of a build area. Asreferred to herein, a build area refers to a two-dimensionalcross-section of a build volume. In the example of FIG. 9B, for example,a build area may include some or all of the surface of container 906.For instance, the build area may be defined by those portions of thecontainer that the light 922 may be directed toward. As may beappreciated, the techniques disclosed herein may be suited for use inany additive fabrication techniques in which parts are formed from aphotocurable material, and are not limited to the illustrative invertedstereolithography approach illustrated in FIGS. 9A-9B. For instance, thetechniques may also be applied in so-called right-side up approaches tostereolithography.

In the example of FIGS. 9A-B, directing light to the build area exposesliquid photopolymer 910 to actinic radiation and cures a thin layer ofthe liquid photopolymer, which causes it to harden. In FIG. 9B, the mostrecently cured layer is referenced as layer 914. When the layer 914 isformed, it is at least partially in contact with the surface of thecontainer 906. The other side of layer 914 bonds with a previously curedlayer in addition to the transparent floor of the container 906. Inorder to form additional layers of the part subsequent to the formationof layer 914, any bonding that occurs between the transparent floor ofthe container 906 and the layer 914 must be broken. For example, one ormore portions of the surface (or the entire surface) of layer 914 mayadhere to the container 906 such that the adhesion must be removed priorto formation of a subsequent layer.

In order to cure the layer 914 by exposure to actinic radiation, thestereolithographic printer 900 may use the laser 916 and scanner system918 to produce a laser beam 922. The laser 916 can produce laser lightrays 920 which are directed to the scanner system 918. The scannersystem 918 directs a laser beam 922 to a location of the build volume.The laser beam 922 may have a spot size within the build volume based onthe cross-sectional size of the laser beam at the point where the beamis incident on the build volume. Exposure of a portion of the liquidphotopolymer 910 to the laser cures the portion of the liquidphotopolymer. For example, when an entire portion of the build volume oflayer 914 has been exposed to the laser beam 922, layer 914 of the part912 may be formed. The scanner system 918 may include any number andtype of optical components, such as multiple galvanometers and/or lensesthat may be operated to direct the light emitted by laser 916.

In conventional stereolithography systems, multiple problems may arisedue to limitations of the light source used in the fabrication system.One challenge with a laser light source is that a laser has a fixed spotsize when incident upon the liquid photopolymer. As such, the spot sizeof the laser when directed to a given position within the build volumeis fixed, no matter the size and shape of the layer to be formed.Additionally, it may take time for a laser beam to scan an area defininga layer of the part. Thus, the fixed spot size and time required forscanning limit the speed at which the laser can be directed to formsolid material, and hence the speed at which the fabrication process canbe completed.

Another problem that may arise in additive fabrication systems that usea laser light source is that the laser beam must be directed to variouspositions within the build volume, which are generally positioned atdifferent distances from the laser source. Thus, the optical path lengthfrom the laser source to the location at which liquid photopolymer is tobe cured will vary across the build volume. This may cause laser beamsand their associated optics to produce a less well-defined (e.g. morediffuse) spot of light at greater optical path lengths, and/or may alsocomplicate fabrication due to the light being incident on the buildvolume at a range of different angles, thereby creating differentlyshaped spots of light. These issues may be exacerbated for longer pathlengths and consequently, directing the laser beam to exterior regionsor regions far from the light source of the build volume (e.g., thosenear the sides of container 906) may result in solid material beingformed in those exterior regions in a less precise manner (e.g., due tothe spot of light being less distinct).

In many additive fabrication devices, this limitation of a laser sourceplaces a practical upper limit on the size of the build area forlaser-based systems. Some conventional systems alternately employ adigital light processing (DLP) source as the light source in an additivefabrication device, which can produce light that has the same opticalpath length to all points in the build volume and can expose a largerportion (e.g., all) of a build area to actinic radiation simultaneously.This can reduce overall build time, however DLP light sources contain afixed array of light sources such that their light is directed only tofixed locations within the build volume, such that there may belocations in the build volume to which light cannot be directly appliedor cannot be applied with desired accuracy. Furthermore, as the buildvolume increases, the accuracy of the DLP light source may decrease asthe light must travel a longer distance and may diverge over the longerdistance.

The inventors have recognized and appreciated that a light source thatcan be moved across the build area would mitigate the above-describedissues by allowing light to be directed to any desired position withinthe build area by moving the light source. This configuration may alsoallow the distance from the light source to the build volume (theoptical path length) to be substantially the same for each positionacross the build area by moving the light source whilst maintaining afixed distance from the light source to the build volume. Thisconfiguration may allow for fabrication of larger parts in an additivefabrication device by eliminating the practical upper limit on the areaof the build volume that can be imposed by use of a laser light source,as discussed above.

While the above-described techniques for application of light may besuited for use in systems in which the liquid photopolymer is held in acontainer with a rigid bottom surface, additional problems may arisewhere the container includes a flexible bottom surface, such as a film.In such systems, layers of a part being fabricated may be distorted as aresult of distortions in the flexible surface. For example, in system900, the bottom surface of the container 906 may be formed from (or maycomprise) a film that could be distorted as a result of various forces,such as the platform 904 applying a downward force into the liquid(e.g., by pushing part 912 into the container) and/or by the weight ofthe liquid photopolymer causing the film to sag. Such a distortion inthe surface of the container 906 may result in portions of the layer 920being formed thicker or thinner than desired, since there may no longerbe flat, parallel surfaces exhibited between the part 912 and the areasof the container 906 on to which solid material is formed.

The inventors have recognized and appreciated that a mechanism tocounteract distortions in the surface of the container 906 may therebyreduce distortions in a fabricated part. In particular, levelingelements such as rollers may be moved laterally across the build areawhilst providing an upward force upon the flexible surface, therebyproducing a sufficiently flat surface for fabrication to proceed.Furthermore, the inventors have recognized and appreciated that anadditive fabrication device may be configured to include a moveablestage on which both the above-described leveling element(s) and one ormore light sources are disposed. Accordingly, the resulting moveablestage may provide a light source that can be moved across the build areain concert with one or more leveling elements that apply a force to aflexible portion of the container.

According to some embodiments, a moveable stage may comprise one or morearrays of light sources, such as arrays of light emitting diodes (LEDs).In some implementations, the size of an area of light within the buildvolume illuminated by a light source can be adjusted by (1) includinglight sources producing beams of various different sizes (e.g., arrayseach producing beams of a different size) within the moveable stage andactivating selected light sources to produce a desired beam size, and/or(2) by moving one or more of the light sources towards or away from thebuild volume. A variable illumination area may decrease fabricationtimes by enabling an additive fabrication device to utilize a largerspot size to fill in larger areas and a smaller spot size to fill insmaller areas when forming solid material. In some embodiments, each ofthe light sources may produce beams of the same sizes and a desired beamarea may be produced by activating one or more individual beams.

Following below are more detailed descriptions of various conceptsrelated to, and embodiments of, directing a source of light in additivefabrication and associated methods. It should be appreciated thatvarious aspects described herein may be implemented in any of numerousways. Examples of specific implementations are provided herein forillustrative purposes only. In addition, the various aspects describedin the embodiments below may be used alone or in any combination, andare not limited to the combinations explicitly described herein.

Although the embodiments herein are primarily disclosed with respect tostereolithography systems, the techniques described herein may beequally applicable to other systems that produce solid material throughapplication of actinic radiation. In some embodiments, structuresfabricated via one or more additive fabrication techniques as describedherein may be formed from, or may comprise, a plurality of layers. Forexample, layer-based additive fabrication techniques may fabricate apart by forming a series of layers, which may be detectable throughobservation of the part, and such layers may be any size, including anythickness between 10 microns and 500 microns. In some use cases, alayer-based additive fabrication technique may fabricate a part thatincludes layers of different thicknesses.

FIG. 1A illustrates a light source 100 suitable for illumination withina stereolithographic additive fabrication device, according to someembodiments. In the example of FIG. 1A, light source 100 includes twolight-emitting diode (“LED”) arrays 101 which each comprise electrodes103A and 103B and multiple rows of the LED emitters 104. In theillustrated configuration, four rows of LEDs are staggered or offsetwith respect to neighboring rows in each of the two LED arrays, as shownin FIG. 1A, which may improve reliability and resolution of an additivefabrication device into which the device 100 is installed. In theexample of FIG. 1A, the electrodes 103A may be, for instance, a commoncathode and the electrodes 103B may be anodes each coupled to arespective LED.

For example, the spacing of LEDs, and thus the ultimate resolution of aprint, may be restricted by how many LEDs can fit into a single row. Insome embodiments, such restrictions may be addressed by placing LEDs inparallel rows, staggered such that an area of the resin that is notilluminated by a first row of LEDs may be illuminated by one or morestaggered rows. LED arrays, which may consist of such staggered rows,are then attached to a frame 102. According to some embodiments, theframe 102 may be coupled to, or may form part of, a moveable stage asdiscussed above.

As may be understood, the construction of LED arrays is not limited toany specific geometries or dimensions. LED arrays may be configured intoany shape or size. As may be appreciated, certain configurations may bemore advantageous for certain desired parameters such as speed, orsimplicity while alternative configurations may be more advantageous forparameters such as cost or flexibility. For example in an arrangementprioritizing speed of printing and valuing simplicity, it may beadvantageous to include an LED array the size of the full print area inorder to reduce motion and allow the full printable area to beilluminated at once. In an arrangement prioritizing flexibility andcost, it may be more advantageous to include one or more smaller LEDarrays in order to reduce the cost and add flexibility for suitingdifferent printing needs such as adjusting the resolution for differentapplications.

In some embodiments, one or more arrays of LED emitters 104 may becollectively connected to a common cathode 103. Some embodiments mayinclude an imaging lens 105, as shown in FIG. 1B, which may be suspendedover some or all of the emitters in an array, and may be suspended oversome or all of the arrays in the device. In some embodiments, variousdifferent numbers of cathodes 103 and imaging lenses 105 and LEDemitters 104 may be employed, as well as different arrangements of LEDemitters 104. Irrespective of how these elements are arranged, for easeof explanation, herein, movement of LED arrays 101 will refer to thecollective movement of LED emitters 104, cathode 103, imaging lens 105,and frame 102. As discussed above, such movement may be achieved bymechanically coupling these elements to a moveable stage such that theelements move in concert with one another by moving the moveable stage.These components, however, may also be moved individually orcollectively in any combination as the invention is not limited in thisrespect.

In some embodiments, LED arrays, such as those depicted in FIGS. 1A-1B,may provide comparable fabrication accuracy to that of a laser lightsource. As referred to herein, “accuracy” of a fabricated part may referto a measure of similarity between a fabricated part and athree-dimensional model from which instructions to fabricate the partwere generated. Since a three-dimensional model is not a physicalobject, it can exhibit details at any scale, whilst a fabricated objectmay have practical lower bounds on the sizes of various features thatcan be formed. As such, additive fabrication devices may not generallyproduce parts having complete accuracy compared with respectivethree-dimensional models from which instructions to fabricate a partwere generated. Nonetheless, various additive fabrication devices andtechniques may produce parts with varying degrees of accuracy, andreferences to improving accuracy herein may denote that a describedtechnique(s) enables a closer replication of the part with respect tothe three-dimensional model from which instructions to fabricate thepart were generated than would otherwise be produced in the absence ofthe technique(s). Note that the described techniques may improveaccuracy for some, but not necessarily all, parts.

FIG. 2 depicts a cross-sectional view showing operation of anillustrative arrangement of light sources and an imaging lens, accordingto some embodiments. A portion of a stereolithographic device 200 isshown in FIG. 2 , and includes light sources 201 arranged on a moveablestage 202, and a lens 205 arranged to direct light from the lightsources 201 onto a liquid photopolymer 209. It will be appreciated thatthe liquid photopolymer may be held in a suitable container in device200, but this component is not shown in FIG. 2 for purposes of clarity.

According to some embodiments, light sources 201 may include one or moreLEDs (e.g., one or more LED arrays as shown in FIG. 1A), which arelambertian light sources. In such a light source, the beams from thelight source tend to diverge, as illustrated by the diverging radiation206 which diverges from respective light sources 201 in FIG. 2 . Thefurther the target of radiation is from the LED, the more the radiationis likely to diverge before it reaches the target. Moving the LED awayfrom the target may therefore result in an increase in spot size, whichmay decrease accuracy of the light source and the intensity of the lightsource, which may impact the ability of an LED to cure the resinaccurately and within the timeframe required. To mitigate this issue, insome embodiments, an imaging lens 205 may counteract this divergence inradiation by imaging the LED radiation 207 onto a liquid photopolymer(e.g., liquid photopolymer resin) 209.

According to some embodiments, imaging lens 205 may refocus divergedradiation to decrease the spot size and/or may increase the intensity ofthe light produced by the light sources 201. In effect, the accuracy ofradiation from light sources 201 may be reconstructed by an imaging lens205. Additionally, light sources 201 may collectively radiate a largerarea of a liquid photopolymer by using multiple light beams instead ofbeing limited to a single beam. These light beams or emitters may varyin beam size, and the radiated area may be adjusted by varying one ormore of: the size of the light sources, the number of light sources perarray and/or the number of light sources.

An illustrative embodiment of an inverse stereolithographic printercomprising a moveable stage comprising light sources is depicted in FIG.3A. In the example of FIG. 3A, stereolithographic printer 300 comprisesbuild platform 312, support structure 313, liquid photopolymer 309,supports 311, rollers 308, imaging lens 305, LED arrays 301, and frame302. The build platform 312 upon which a part is formed, is attached toa support structure 313 which is configured to move the build platform312 relative to the liquid photopolymer 309 along the Z-axis. The liquidphotopolymer 309 rests on top of film 310 and between supports 311forming an area that can be referred to as the vat 314. In someembodiments, portions of the film 310 may be transparent to actinicradiation, such that actinic radiation can be targeted at portions ofthe liquid photopolymer 309 through the film 310. The frame 302 maysupport and move LED arrays 301 within the printer, and an imaging lens305 may focus the radiation from the LED arrays.

In some embodiments, a part may be formed layer wise onto the buildplatform 312 by the repetition of a sequence of steps in the buildingprocess. In the illustrative process shown, the build platform 312 maybe lowered into the vat along the Z-axis. In some cases, the downwardmotion of the build platform 312 may tend to push liquid photopolymer309 towards the bottom of the vat 314. This fluid motion may exert forceagainst the bottom of the vat, causing a distorted region to form,wherein the film 310 may no longer be relatively flat. This distortedregion, discussed further below, represents an area withgreater-than-desired thickness of liquid photopolymer 309. Proceedingwith curing of the photopolymer in this region may therefore result inlayers of inconsistent thickness, potentially leading to unwanteddistortion in the part and/or failure in part formation.

For instance, FIG. 4 depicts an exaggerated illustration of a distortedregion within a film, according to some embodiments. A portion of astereolithographic printer 400 is shown, in which a film 410 includes adistorted region 415. A build platform 412 and support structure 413 areshown for context.

Conventional systems may address a distortion in the film by utilizing awiper as a levelling element. In such systems, a wiper may move alongthe X-axis through the area of the distortion. This interaction with thefilm 310 may result in the formation of a substantially flattenedinterface region in the area trailing the levelling element as it movesthrough the area previously occupied by the distortion. However, it maybe necessary to wait until the wiper has travelled across the entirelength of the film 310 and reversed back to its original position beforeexposing material to radiation. This delay between the interaction ofthe wiper and film 310 and the radiation may result in the formation ofnew distortions of the film during the interval.

In some embodiments, these issues and others may be addressed by the useof rollers 308 as leveling elements to limit this lag. Rollers 308 maykeep the portion of the film 310 directly above the light sources 301taut and thus relatively flat. This is illustrated in FIG. 3A where onlythe portion of the film 310 between the rollers 308 are relatively flat,whereas the other areas of the film 310 are comparatively loose. Whenrollers 308 shift, so does the portion of the film 310 that is taut, asshown in FIG. 3B, which illustrates system 300 with the rollers andmoveable stage in a different position along the X-axis compared withFIG. 3A. The rollers 308, directly below a film 310, may exert an upwardforce which may counteract the downward force of the build platform 312and liquid photopolymer 309. According to some embodiments, rollers 308may be coupled to the moveable stage 302 either directly or via one ormore other mechanical elements. In some embodiments, the rollers 308 andthe movable stage may be mounted on, or otherwise coupled to, a commonelement, such as a housing, which is configured to move in the X-axisdirection, thereby carrying the moveable stage and rollers with themotion.

Moving light sources 301 with the rollers 308 may advantageously reducethe amount of time between positioning by the rollers and exposure toradiation from the light source, thus reducing any potential distortionin that time interval. An added advantage to this concerted movement oflevelling element and light source is that the film 310 that is notdirectly above the rollers 308 and the area between the rollers 308 mayloosen and gradually “peel” any portion of the part that has beenprinted away from it. This approach causes the film 310 to have a curvedsurface relative to the region of contact between the solid material andsupporting liquid photopolymer 309. The curved surface of the film 310may allow for a gradual and/or even application of force that aids inminimizing forces applied to the part to remove the adhesion between thepart and the surface of the container 311. This passive peel employingthe bending of the film 310 may help decrease the adhesive forcesbetween the solid printed material and the supporting photopolymerliquid immediately after formation of the solid material. This decreasein adhesive forces may serve several advantages, including allowing aweaker force to be used in raising the build platform 312.

Moreover, rollers may possess a number of potential advantages comparedwith static protrusions, including both a minimal profile for thecontact area between the element and the film and the ability to “roll,”rather than slide, in response to any frictional forces exerted by thefilm. In some cases, however, rollers may be disfavored overall becauseof the demand for small tolerances so that flat surfaces areconsistently produced at the same height. Such exacting tolerances maybe difficult and expensive to meet in practice. The inventors have,however, recognized and appreciated a roller element design that canproduce a sufficiently flat film surface without it being necessary foreach component of the roller elements to individually be produced atsuch small tolerances. In particular, a roller may be formed from anumber of roller segments arranged along a common axis. The rollersegments may be coupled to one another and/or may be held within asuitable structure that allows independent rotation of each rollersegment.

As one example, FIGS. 3C-3D depict an illustrative moveable stage thatincludes segmented rollers, according to some embodiments. In theexample of moveable stage 359 shown in FIG. 3C, each of the two picturedroller elements 361 comprise four roller segments 362. Moveable stage359 may be included, for instance, as the moveable stage depicted instereolithographic printer 300 of FIGS. 3A-3B (e.g., the stagecomprising elements 301, 302, 305 and 308) such that the roller segments362 extend along the Y axis of the device 300, perpendicular to both theX-Axis and Z-Axis.

In the example of FIGS. 3C-3D, roller segments 362 may each be formedfrom any suitable material or materials, but may preferably comprisecomparatively incompressible and wear resistant materials, such asaluminum, stainless steel (e.g., 303 grade stainless steel), chromesteel, and/or other grades of steel commonly used for bearings. In someembodiments, roller segments 362 may be treated with one or more coatingmaterials, such as one or more ceramics, titanium nitride, chrome, orcombinations thereof. In some implementations, roller segments 362 mayinclude bearing steel rods of approximately 3-10 mm, with each rodhaving a length of between 20 mm and 60 mm. In some implementations, themoveable stage 359 may include four roller segments within each rollerelement, with the segments having individual lengths of 45 mm and adiameter of 6.35 mm. Although shown to be of equal lengths in theexample of FIGS. 3C-3D, the lengths of the roller segments may ingeneral differ from one another. It will be appreciated that the use offour roller segments in the illustrative roller elements is provided asone example, and any number of roller segments 362 may in general bearranged within each roller element 361.

In the example of FIG. 3C, spacers 367 are provided to maintain apredefined separation distance between roller segments 362, which mayact to prevent wear and other contact interactions between rollersegments 362. In some embodiments, such spacers may be flexiblecouplings, such as silicone adhesive connecting roller segments 362. Insome embodiments, spacers 367 may include an independently movableelement, such as a ball bearing.

As shown in the example of FIG. 3D, a roller segment 362 may be disposedwithin a retaining feature 368. According to some embodiments, theroller segment may be attached to the retaining feature or to some otherpart of the moveable stage 359, or may be held in the retaining featurewithout attachment. Retaining features 368 may act to limit the range ofmotion of roller segments 362. In particular, as shown in the example ofFIG. 3D, the retaining feature 368 may include overhangs or “fingers”370, which may limit the lateral and/or upward range of motion of theroller segment 362. The retaining feature 368 may further include asupporting base portion 369 that limits the downwards range of motion ofthe roller segment.

In some embodiments, retaining features 368 may comprise a low-frictionand/or wear-resistant material, such as nylon, polyacetal,polytetrafluoroethylene (PTFE), ultra-high-molecular-weight polyethylene(UHMWPE), and/or PEEK, allowing the roller segment 362 to move againstthe fingers 370 and supporting base 369. It should be noted, however,that it is not necessary for the roller segments 362 to actually rollcontinually or at all during operation, though such rolling may reducethe lateral forces exerted against a film. In general, the inventorshave found that a small amount of clearance between the retainingfeatures 368 and roller segments 362 to be advantageous. In particular,a clearance between the retaining features 368 and roller segments 362may be between 10 μm and 50 μm, or between 20 μm and 40 μm, or less than50 μm.

In some embodiments, the roller segments 362 may have less than 200 μmof clearance to move in the Z axis against the fingers 370 of theretaining features 368 and less than 50 μm of clearance to move in the Xaxis against the sides of the retaining features 368. In someembodiments, roller segments 362 may be constrained from motion awayfrom the supporting base 369 by the tension of a film in contact withthe roller segment 362.

In some embodiments, fingers 370 may extend over the roller segment 362a sufficient amount to restrict the motion of the roller segment. Inaddition, or alternatively, ends of roller segments 362 may be shaped invarious ways to minimize unwanted interactions between segments adjacentto one another along the Y axis. In some embodiments, a cylindricalspacing region may be formed at the ends of each roller segment, thespacing regions having a diameter smaller than the diameter of thenon-spacing regions of the roller. In some embodiments, a narrowedpositive feature formed by such a narrowed cylindrical segment may bepaired with a negative feature in the abutting roller formed by acylindrical recess, thus partially interlocking the roller segments 362.The sides of the roller segments 362 may further incorporate chamfers orother features, but are preferably polished so as to avoid sharp edgesthat may increase wear against the film 103.

The inventors have recognized and appreciated that roller segments 362allow for the roller segments to have significantly larger dimensionaltolerances, such as straightness or average diameter, compared with thetolerances usually necessary for a roller element to produce a desiredfilm flatness. As discussed above, a roller elements generally demandsmall tolerances so that flat surfaces are consistently produced at thesame height. A roller element comprising roller segments may, however,produce a consistently flat film surface even though a consistently flatfilm surface would not result if the same cylindrical material were usedas a single piece roller element.

For instance, small deviations in straightness, such as a bend, in asingle long roller may result in a significant displacement of thesurface of the roller from the midline at the midpoint of the roller.The same degree of deviation in straightness, however, in a shorterlength of roller, may result in a much smaller total displacement in thesurface of the roller from the midline of at the midpoint of the shorterroller. Accordingly, the use of multiple, and thus shorter, rollersegments 362, allows for smaller total displacements, even with the sametolerances in straightness. A much wider range of tolerances maytherefore be acceptable in the roller segments 362. In other words, thedimensional tolerance of the retaining features, particularly withregards to the supporting base 369, may be the primary influence on theprecision and accuracy of the motion of the roller segments, rather thanthe dimension tolerances of the roller segments themselves. Theprovision of a uniformly flat and level supporting base 369 (withrespect to the XY build plane), however, may be considerably easier andless expensive.

As an alternative to the depicted segmented cylindrical roller segments362, in some embodiments, one or more different segment structures maybe combined to form a roller segment. For instance, circular ballbearings and/or flexible rods may be arranged in place of theillustrative cylindrical roller segments. Conceptually, a sufficientlyflexible rod may decouple the deflection and/or deviation at a givenportion of the rod from more distant points on the rod. In someembodiments, an otherwise inflexible rod may be modified by the additionof circular cuts spaced along the length of the rod. As one example, arelatively inflexible rod having a diameter of 6.35 mm and length of 200mm may be modified by making radial cuts, or trenches, of approximately2 mm into the rod spaced 40 mm apart along the length of the rod. Theremaining core of the rod, having a diameter of 2.35 mm, may becomparatively more flexible than the full width rod and allows for aform of segmentation, whereby unmodified regions of the rod locatedbetween trenches are capable of a decoupling deflection at the regionsthinned by trenches.

In some embodiments, roller segments 362 may be supported and/orinterconnected along a common axis. As one example, roller segments 362may include a cylindrical hole running lengthwise through the segments362 and a mounting device, such as a thin rod or flexible wire, may runthrough a group of segments 362 through such a cylindrical hole.Alternatively, or additionally, roller segments 362 may include a seriesof protrusions and depressions on abutting ends, such that a protrudingportion of a first roller segment 362 may extend partially into adepressed portion of an adjacent roller segment 362.

In the example of FIG. 3C, moveable stage 359 further comprises one ormore light sources forming exposure source 360 located between rollerelements 362. The exposure source 360 may be configured as a lineararray of light emitting elements, such as the LED arrays describedabove.

While some embodiments described herein employ rollers as levelingelements, it should be appreciated that rollers are described as but oneexample of a leveling element, and that any other structure or geometrythat serves the purpose of leveling the film 310 may be used in place ofany one or more of the rollers. As such, it will be appreciated that,for any embodiments described herein that includes one or more rollers,any other suitable leveling element may be substituted for any one ormore of the rollers, as the techniques described herein are not limitedto any particular type of leveling element.

Leveling elements (e.g., rollers) may be configured in various ways, anexample of which is illustrated in FIGS. 5A-5C, which depict twostraight parallel rollers. In some embodiments, cylinders areadvantageous because they are easy to move by rolling and/or sliding.Though other shapes and structures may also be capable of suchmovements, cylinders, or near cylinders, may have several advantages.For example, cylinders or near cylinders may experience less opposingfriction than rollers with a sharp edge, such as rectangular prisms.Cylinders or near cylinders may also maintain the integrity of the filmby not leaving imprints or scratches from the sharp edges. Structuresand shapes with additional faces approaching a cylindrical shape mayprovide advantages as leveling elements such as ensuring a stricttolerance. In some embodiments, a coating or film can also be includedto further limit friction. The coating or film can be applied to asurface of the leveling elements to reduce friction.

In some embodiments, the use of LED arrays and roller members, such asdescribed above, may be combined. In such embodiments, the light sourcemay be configured to move with the rollers. As one example, the arraysmay move with the rollers in the Y-direction, as shown in FIGS. 5A-5C.In the example of FIG. 5C, rollers 508 are arranged with a moveablestage 502 in between on which two light sources 501 (e.g., LED arrays)are arranged beneath a lens 505. It will be appreciated that additionalcomponents to produce motion of the rollers and moveable stage may alsobe included but are not shown in FIGS. 5A-5C for clarity.

In some cases, multiple arrays of light sources may be arranged ontodifferent moveable stages that may be independently moved and operatedto produce light. The inventors have appreciated that having multipleoptions for scalability by adding additional arrays or modifying thearray to have multiple emitter sizes or alternative LED arrangements mayallow for additional flexibility or a more linear increase incost/increased output as compared to adding an entirely new laser in anadditive fabrication device that employs a laser light source or a newprojector in an additive fabrication device that employs a DLPprojector.

An illustrative embodiment of motion of multiple LED arrays coupled tomultiple sets of rollers is depicted in FIGS. 6A-C. FIG. 6A depicts foursets of light sources (e.g., four pairs of LED arrays) 601 which can allmove along both the X-axis and the Y-axis. FIG. 6B illustrates the foursets of light sources after movement along the Y-axis and FIG. 6Cillustrates movement along the X-axis. By including multiple sets ofrollers with multiple LED arrays coupled to the rollers, the efficiencywith which a part is fabricated may significantly improve over that ofconventional systems. For example, multiple portions of a build volumecan be simultaneously exposed to a light source. This may significantlydecrease the time to fabricate a part.

FIG. 7 illustrates an embodiment with a roller in a ring geometry,according to some embodiments. System 700 includes light sources 701arranged on a moveable stage 702 beneath a lens 705. A ring-shapedroller 708 is arranged around the moveable stage and may be configuredto move in both the X-axis and Y-axis directions along with the moveablestage. A roller in a ring geometry may have more degrees of freedom thanrollers in a straight line geometry. In some embodiments, the additivefabrication device may include a plurality of rollers of a ringgeometry. The plurality of rollers may move simultaneously across abuild area of the additive fabrication device. Rollers of a ringgeometry may further move in different directions and may expedite theprinting process even further.

FIG. 8 illustrates a stereolithographic printer 800 that includes acooling fan beneath the light sources. In the example of FIG. 8 , lightsources 801 (e.g., LED arrays) are arranged on moveable stage 802beneath a lens 805 and are configured to move beneath the containerformed by film 810 and walls 811 along with the rollers 808. Thecontainer holds liquid photopolymer 809 and the printer is configured toform parts on the build platform 812, supported by support structure813.

In the example of FIG. 8 , a heat sink 817 and cooling fan 816 arearranged beneath the light sources 801. Since some light sources, suchas LEDs, radiate via an exothermic reaction, a heat sink and/or acooling fan can absorb the heat produced and help to control thetemperature of the additive fabrication device in general and the LEDarray in particular. This may allow a longer lifetime of LED arraysand/or additive fabrication devices.

While a moveable stage may extend over any suitable portion of a buildarea, FIG. 10 illustrates one embodiment wherein LED arrays 1001 areconfigured to extend across one full dimension of the build area 1004.That is, the LED arrays (or at least the moveable stage on which the LEDarrays are arranged) extends completely over one dimension of the buildarea, such as the width, and may in some cases extend further. Thisarrangement of light sources is referred to herein as a Linear LEDArray. In the example of FIG. 10 , the LED arrays 1001 (which may each,for instance, be one of the LED arrays 101 shown in FIG. 1A) aredepicted with space between then along the moveable stage. However, insome embodiments the LED arrays may be lined up end to end toeffectively produce a single large array of LEDs.

In the example of FIG. 10 , the Linear LED array 1001 is aligned alongone axis such that the movement of the Linear LED array 1001 coupledwith a moveable stage 1002 is limited to one axis 1003. As may beappreciated by one skilled in the art, it may be advantageous to movethe stage along a single axis, in this case the x-axis. As may befurther appreciated the Linear LED array could be comprised of onecontinuous LED array, or multiple smaller LED arrays arranged together.The LED arrays could be made up of one row of LEDs, or multiple rows ofLEDs arranged in a line or in a staggered configuration. Thisarrangement may be coupled with any other configurations describedherein including the use of multiple Linear LED Arrays

FIG. 11 is a block diagram of a system suitable for practicing aspectsof the invention, according to some embodiments. System 1100 illustratesa system suitable for generating instructions to perform additivefabrication by an additive fabrication device and subsequent operationof the additive fabrication device to fabricate an object. For instance,instructions to activate or deactivate light sources, move a moveablestage, etc. as described by the various techniques above may begenerated by the system and provided to the additive fabrication device.Various parameters associated with operation of a moveable stage may bestored by system computer system 1110 and accessed when generatinginstructions for the additive fabrication device 1120 to fabricate apart.

According to some embodiments, computer system 1110 may execute softwarethat generates two-dimensional layers that may each comprise sections ofan object. Instructions may then be generated from this layer data to beprovided to an additive fabrication device, such as additive fabricationdevice 1120, that, when executed by the device, fabricates the layersand thereby fabricates the object. Such instructions may be communicatedvia link 1115, which may comprise any suitable wired and/or wirelesscommunications connection. In some embodiments, a single housing holdsthe computing device 1110 and additive fabrication device 1120 such thatthe link 1115 is an internal link connecting two modules within thehousing of system 1100.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated that various alterations,modifications, and improvements will readily occur to those skilled inthe art. Such alterations, modifications, and improvements are intendedto be part of this disclosure, and are intended to be within the spiritand scope of the invention. Further, though advantages of the presentinvention are indicated, it should be appreciated that not everyembodiment of the technology described herein will include everydescribed advantage. Some embodiments may not implement any featuresdescribed as advantageous herein and in some instances one or more ofthe described features may be implemented to achieve furtherembodiments. Accordingly, the foregoing description and drawings are byway of example only.

FIG. 12 illustrates an example of a suitable computing systemenvironment 1200 on which the technology described herein may beimplemented. For example, computing environment 1200 may form some orall of the computer system 1110 shown in FIG. 11 . The computing systemenvironment 1200 is only one example of a suitable computing environmentand is not intended to suggest any limitation as to the scope of use orfunctionality of the technology described herein. Neither should thecomputing environment 1200 be interpreted as having any dependency orrequirement relating to any one or combination of components illustratedin the exemplary operating environment 1200.

The technology described herein is operational with numerous othergeneral purpose or special purpose computing system environments orconfigurations. Examples of well-known computing systems, environments,and/or configurations that may be suitable for use with the technologydescribed herein include, but are not limited to, personal computers,server computers, hand-held or laptop devices, multiprocessor systems,microprocessor-based systems, set top boxes, programmable consumerelectronics, network PCs, minicomputers, mainframe computers,distributed computing environments that include any of the above systemsor devices, and the like.

The computing environment may execute computer-executable instructions,such as program modules. Generally, program modules include routines,programs, objects, components, data structures, etc. that performparticular tasks or implement particular abstract data types. Thetechnology described herein may also be practiced in distributedcomputing environments where tasks are performed by remote processingdevices that are linked through a communications network. In adistributed computing environment, program modules may be located inboth local and remote computer storage media including memory storagedevices.

With reference to FIG. 12 , an exemplary system for implementing thetechnology described herein includes a general purpose computing devicein the form of a computer 1210. Components of computer 1210 may include,but are not limited to, a processing unit 1220, a system memory 1230,and a system bus 1221 that couples various system components includingthe system memory to the processing unit 1220. The system bus 1221 maybe any of several types of bus structures including a memory bus ormemory controller, a peripheral bus, and a local bus using any of avariety of bus architectures. By way of example, and not limitation,such architectures include Industry Standard Architecture (ISA) bus,Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, VideoElectronics Standards Association (VESA) local bus, and PeripheralComponent Interconnect (PCI) bus also known as Mezzanine bus.

Computer 1210 typically includes a variety of computer readable media.Computer readable media can be any available media that can be accessedby computer 1210 and includes both volatile and nonvolatile media,removable and non-removable media. By way of example, and notlimitation, computer readable media may comprise computer storage mediaand communication media. Computer storage media includes volatile andnonvolatile, removable and non-removable media implemented in any methodor technology for storage of information such as computer readableinstructions, data structures, program modules or other data. Computerstorage media includes, but is not limited to, RAM, ROM, EEPROM, flashmemory or other memory technology, CD-ROM, digital versatile disks (DVD)or other optical disk storage, magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices, or any othermedium which can be used to store the desired information and which canaccessed by computer 1210. Communication media typically embodiescomputer readable instructions, data structures, program modules orother data in a modulated data signal such as a carrier wave or othertransport mechanism and includes any information delivery media. Theterm “modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, RF, infrared and otherwireless media. Combinations of the any of the above should also beincluded within the scope of computer readable media.

The system memory 1230 includes computer storage media in the form ofvolatile and/or nonvolatile memory such as read only memory (ROM) 1231and random access memory (RAM) 1232. A basic input/output system 1233(BIOS), containing the basic routines that help to transfer informationbetween elements within computer 1210, such as during start-up, istypically stored in ROM 1231. RAM 1232 typically contains data and/orprogram modules that are immediately accessible to and/or presentlybeing operated on by processing unit 1220. By way of example, and notlimitation, FIG. 12 illustrates operating system 1234, applicationprograms 1235, other program modules 1236, and program data 1237.

The computer 1210 may also include other removable/non-removable,volatile/nonvolatile computer storage media. By way of example only,FIG. 12 illustrates a hard disk drive 1241 that reads from or writes tonon-removable, nonvolatile magnetic media, a flash drive 1251 that readsfrom or writes to a removable, nonvolatile memory 1252 such as flashmemory, and an optical disk drive 1255 that reads from or writes to aremovable, nonvolatile optical disk 1256 such as a CD ROM or otheroptical media. Other removable/non-removable, volatile/nonvolatilecomputer storage media that can be used in the exemplary operatingenvironment include, but are not limited to, magnetic tape cassettes,flash memory cards, digital versatile disks, digital video tape, solidstate RAM, solid state ROM, and the like. The hard disk drive 1241 istypically connected to the system bus 1221 through a non-removablememory interface such as interface 1240, and magnetic disk drive 1251and optical disk drive 1255 are typically connected to the system bus1221 by a removable memory interface, such as interface 1250.

The drives and their associated computer storage media discussed aboveand illustrated in FIG. 12 , provide storage of computer readableinstructions, data structures, program modules and other data for thecomputer 1210. In FIG. 12 , for example, hard disk drive 1241 isillustrated as storing operating system 1244, application programs 1245,other program modules 1246, and program data 1247. Note that thesecomponents can either be the same as or different from operating system1234, application programs 1235, other program modules 1236, and programdata 1237. Operating system 1244, application programs 1245, otherprogram modules 1246, and program data 1247 are given different numbershere to illustrate that, at a minimum, they are different copies. A usermay enter commands and information into the computer 1210 through inputdevices such as a keyboard 1262 and pointing device 1261, commonlyreferred to as a mouse, trackball or touch pad. Other input devices (notshown) may include a microphone, joystick, game pad, satellite dish,scanner, or the like. These and other input devices are often connectedto the processing unit 1220 through a user input interface 1260 that iscoupled to the system bus, but may be connected by other interface andbus structures, such as a parallel port, game port or a universal serialbus (USB). A monitor 1291 or other type of display device is alsoconnected to the system bus 1221 via an interface, such as a videointerface 1290. In addition to the monitor, computers may also includeother peripheral output devices such as speakers 1297 and printer 1296,which may be connected through an output peripheral interface 1295.

The computer 1210 may operate in a networked environment using logicalconnections to one or more remote computers, such as a remote computer1280. The remote computer 1280 may be a personal computer, a server, arouter, a network PC, a peer device or other common network node, andtypically includes many or all of the elements described above relativeto the computer 1210, although only a memory storage device 1281 hasbeen illustrated in FIG. 12 . The logical connections depicted in FIG.12 include a local area network (LAN) 1271 and a wide area network (WAN)1273, but may also include other networks. Such networking environmentsare commonplace in offices, enterprise-wide computer networks, intranetsand the Internet.

When used in a LAN networking environment, the computer 1210 isconnected to the LAN 1271 through a network interface or adapter 1270.When used in a WAN networking environment, the computer 1210 typicallyincludes a modem 1272 or other means for establishing communicationsover the WAN 1273, such as the Internet. The modem 1272, which may beinternal or external, may be connected to the system bus 1221 via theuser input interface 1260, or other appropriate mechanism. In anetworked environment, program modules depicted relative to the computer1210, or portions thereof, may be stored in the remote memory storagedevice. By way of example, and not limitation, FIG. 12 illustratesremote application programs 1285 as residing on memory device 1281. Itwill be appreciated that the network connections shown are exemplary andother means of establishing a communications link between the computersmay be used.

The above-described embodiments of the technology described herein canbe implemented in any of numerous ways. For example, the embodiments maybe implemented using hardware, software or a combination thereof. Whenimplemented in software, the software code can be executed on anysuitable processor or collection of processors, whether provided in asingle computer or distributed among multiple computers. Such processorsmay be implemented as integrated circuits, with one or more processorsin an integrated circuit component, including commercially availableintegrated circuit components known in the art by names such as CPUchips, GPU chips, microprocessor, microcontroller, or co-processor.Alternatively, a processor may be implemented in custom circuitry, suchas an ASIC, or semicustom circuitry resulting from configuring aprogrammable logic device. As yet a further alternative, a processor maybe a portion of a larger circuit or semiconductor device, whethercommercially available, semi-custom or custom. As a specific example,some commercially available microprocessors have multiple cores suchthat one or a subset of those cores may constitute a processor. However,a processor may be implemented using circuitry in any suitable format.

Further, it should be appreciated that a computer may be embodied in anyof a number of forms, such as a rack-mounted computer, a desktopcomputer, a laptop computer, or a tablet computer. Additionally, acomputer may be embedded in a device not generally regarded as acomputer but with suitable processing capabilities, including a PersonalDigital Assistant (PDA), a smart phone or any other suitable portable orfixed electronic device.

Also, a computer may have one or more input and output devices. Thesedevices can be used, among other things, to present a user interface.Examples of output devices that can be used to provide a user interfaceinclude printers or display screens for visual presentation of outputand speakers or other sound generating devices for audible presentationof output. Examples of input devices that can be used for a userinterface include keyboards, and pointing devices, such as mice, touchpads, and digitizing tablets. As another example, a computer may receiveinput information through speech recognition or in other audible format.

Such computers may be interconnected by one or more networks in anysuitable form, including as a local area network or a wide area network,such as an enterprise network or the Internet. Such networks may bebased on any suitable technology and may operate according to anysuitable protocol and may include wireless networks, wired networks orfiber optic networks.

Also, the various methods or processes outlined herein may be coded assoftware that is executable on one or more processors that employ anyone of a variety of operating systems or platforms. Additionally, suchsoftware may be written using any of a number of suitable programminglanguages and/or programming or scripting tools, and also may becompiled as executable machine language code or intermediate code thatis executed on a framework or virtual machine.

In this respect, the invention may be embodied as a computer readablestorage medium (or multiple computer readable media) (e.g., a computermemory, one or more floppy discs, compact discs (CD), optical discs,digital video disks (DVD), magnetic tapes, flash memories, circuitconfigurations in Field Programmable Gate Arrays or other semiconductordevices, or other tangible computer storage medium) encoded with one ormore programs that, when executed on one or more computers or otherprocessors, perform methods that implement the various embodiments ofthe invention discussed above. As is apparent from the foregoingexamples, a computer readable storage medium may retain information fora sufficient time to provide computer-executable instructions in anon-transitory form. Such a computer readable storage medium or mediacan be transportable, such that the program or programs stored thereoncan be loaded onto one or more different computers or other processorsto implement various aspects of the present invention as discussedabove. As used herein, the term “computer-readable storage medium”encompasses only a non-transitory computer-readable medium that can beconsidered to be a manufacture (i.e., article of manufacture) or amachine. Alternatively or additionally, the invention may be embodied asa computer readable medium other than a computer-readable storagemedium, such as a propagating signal.

The terms “program” or “software,” when used herein, are used in ageneric sense to refer to any type of computer code or set ofcomputer-executable instructions that can be employed to program acomputer or other processor to implement various aspects of the presentinvention as discussed above. Additionally, it should be appreciatedthat according to one aspect of this embodiment, one or more computerprograms that when executed perform methods of the present inventionneed not reside on a single computer or processor, but may bedistributed in a modular fashion amongst a number of different computersor processors to implement various aspects of the present invention.

Computer-executable instructions may be in many forms, such as programmodules, executed by one or more computers or other devices. Generally,program modules include routines, programs, objects, components, datastructures, etc. that perform particular tasks or implement particularabstract data types. Typically the functionality of the program modulesmay be combined or distributed as desired in various embodiments.

Also, data structures may be stored in computer-readable media in anysuitable form. For simplicity of illustration, data structures may beshown to have fields that are related through location in the datastructure. Such relationships may likewise be achieved by assigningstorage for the fields with locations in a computer-readable medium thatconveys relationship between the fields. However, any suitable mechanismmay be used to establish a relationship between information in fields ofa data structure, including through the use of pointers, tags or othermechanisms that establish relationship between data elements.

Various aspects of the present invention may be used alone, incombination, or in a variety of arrangements not specifically discussedin the embodiments described in the foregoing and is therefore notlimited in its application to the details and arrangement of componentsset forth in the foregoing description or illustrated in the drawings.For example, aspects described in one embodiment may be combined in anymanner with aspects described in other embodiments.

Also, the invention may be embodied as a method, of which an example hasbeen provided. The acts performed as part of the method may be orderedin any suitable way. Accordingly, embodiments may be constructed inwhich acts are performed in an order different than illustrated, whichmay include performing some acts simultaneously, even though shown assequential acts in illustrative embodiments.

Further, some actions are described as taken by a “user.” It should beappreciated that a “user” need not be a single individual, and that insome embodiments, actions attributable to a “user” may be performed by ateam of individuals and/or an individual in combination withcomputer-assisted tools or other mechanisms.

Use of ordinal terms such as “first,” “second,” “third,” etc., in theclaims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another or thetemporal order in which acts of a method are performed, but are usedmerely as labels to distinguish one claim element having a certain namefrom another element having a same name (but for use of the ordinalterm) to distinguish the claim elements.

Also, the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having,” “containing,” “involving,” andvariations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

What is claimed is:
 1. (canceled)
 2. An additive fabrication device configured to form layers of solid material from a liquid photopolymer held in a container, each layer of the solid material being formed so as to contact the container in addition to the surface of a build platform and/or a previously formed layer of material, the additive fabrication device comprising: a container having an interior bottom surface extending in a first direction and a second direction, perpendicular to the first direction; and a movable stage configured to move at least in the first direction, the movable stage being arranged beneath the container and comprising: a plurality of light sources offset from one another along the second direction and operable to direct light through the interior bottom surface of the container; and an imaging lens arranged over the plurality of light sources and configured to converge light from the plurality of light sources onto the liquid photopolymer held in the container.
 3. The additive fabrication device of claim 2, wherein the plurality of light sources is a first plurality of light sources and wherein the imaging lens is a first imaging lens, and wherein the movable stage further comprises: a second plurality of light sources offset from one another along the second direction and operable to direct light through the interior bottom surface of the container; and a second imaging lens arranged over the second plurality of light sources and configured to converge light from the second plurality of light sources onto the liquid photopolymer held in the container.
 4. The additive fabrication device of claim 2, wherein the plurality of light sources comprise a plurality of light sources of a first size and a plurality of light sources of a second size, different from the first size.
 5. The additive fabrication device of claim 4, wherein the plurality of light sources of the first size is offset from the plurality of light sources of the second size along the first direction.
 6. The additive fabrication device of claim 2, wherein the plurality of light sources comprise: a first group of light sources offset from one another along the second direction; and a second group of light sources offset from one another along the second direction and offset from the first group of light sources along the first direction.
 7. The additive fabrication device of claim 6, wherein each of the light sources of the second group of light sources are offset from all of the light sources of the first group of light sources in both the first and the second direction.
 8. The additive fabrication device of claim 2, wherein the movable stage extends over the entire extent of the container along the second direction.
 9. The additive fabrication device of claim 2, wherein the plurality of light sources are a plurality of LEDs.
 10. The additive fabrication device of claim 2, wherein the movable stage is configured to move the plurality of light sources toward or away from the container to adjust an area of light incident upon the liquid photopolymer held in the container.
 11. An additive fabrication device configured to form layers of solid material from a liquid photopolymer held in a container, each layer of the solid material being formed so as to contact the container in addition to the surface of a build platform and/or a previously formed layer of material, the additive fabrication device comprising: a container having an interior bottom surface extending in a first direction and a second direction, perpendicular to the first direction; and a movable stage configured to move at least in the first direction, the movable stage being arranged beneath the container and comprising a plurality of light sources offset from one another along the second direction and operable to direct light through the interior bottom surface of the container, wherein the movable stage is configured to move the plurality of light sources toward or away from the container to adjust an area of light incident upon the liquid photopolymer held in the container.
 12. The additive fabrication device of claim 11, wherein the plurality of light sources comprise a plurality of light sources of a first size and a plurality of light sources of a second size, different from the first size.
 13. The additive fabrication device of claim 12, wherein the plurality of light sources of the first size is offset from the plurality of light sources of the second size along the first direction.
 14. The additive fabrication device of claim 11, wherein the plurality of light sources comprise: a first group of light sources offset from one another along the second direction; and a second group of light sources offset from one another along the second direction and offset from the first group of light sources along the first direction.
 15. The additive fabrication device of claim 14, wherein each of the light sources of the second group of light sources are offset from all of the light sources of the first group of light sources in both the first and the second direction.
 16. The additive fabrication device of claim 11, wherein the movable stage extends over the entire extent of the container along the second direction.
 17. The additive fabrication device of claim 11, wherein the plurality of light sources are a plurality of LEDs.
 18. The additive fabrication device of claim 11, wherein the movable stage further comprises an imaging lens arranged over the plurality of light sources and configured to converge light from the plurality of light sources onto the liquid photopolymer held in the container.
 19. The additive fabrication device of claim 18, wherein the plurality of light sources is a first plurality of light sources and wherein the imaging lens is a first imaging lens, and wherein the movable stage further comprises: a second plurality of light sources offset from one another along the second direction and operable to direct light through the interior bottom surface of the container; and a second imaging lens arranged over the second plurality of light sources and configured to converge light from the second plurality of light sources onto the liquid photopolymer held in the container. 